The present invention relates to complex multi-piece ceramic core assemblies for casting superalloy airfoil castings, such as airfoils having multiple cast walls and complex channels for improved air cooling efficiency.
Most manufacturers of gas turbine engines are evaluating advanced multi-walled, thin-walled turbine airfoils (i.e. turbine blade or vane) which include intricate air cooling channels to improve efficiency of airfoil internal cooling to permit greater engine thrust and provide satisfactory airfoil service life.
U.S. Pat. Nos. 5,295,530 and 5,545,003 describe advanced multi-walled, thin-walled turbine blade or vane designs which include intricate air cooling channels to this end.
In U.S. Pat. No. 5,295,530, a multi-wall core assembly is made by coating a first thin wall ceramic core with wax or plastic, a second similar ceramic core is positioned on the first coated ceramic core using temporary locating pins, holes are drilled through the ceramic cores, a locating rod is inserted into each drilled hole and then the second core then is coated with wax or plastic. This sequence is repeated as necessary to build up the multi-wall ceramic core assembly.
This core assembly procedure is quite complex, time consuming and costly as a result of use of the multiple connecting and other rods and drilled holes in the cores to receive the rods. in addition, this core assembly procedure can result in a loss of dimensional accuracy and repeatability of the core assemblies and thus airfoil castings produced using such core assemblies.
An object of the present invention is to provide a multi-wall ceramic core assembly and method of making same for use in casting advanced multi-walled, thin-walled turbine airfoils (e.g. turbine blade or vane castings) which can include complex air cooling channels to improve efficiency of airfoil internal cooling.
Another object of the present invention is to provide a multi-wall ceramic core assembly and method of making same for use in casting advanced multi-walled, thin-walled turbine airfoils wherein at least a portion of the multi-piece core assembly is formed in novel manner without ceramic adhesive which overcomes disadvantages of the previous core assembly techniques.
The present invention provides, in an illustrative embodiment, a multi-wall ceramic core assembly and method of making same wherein a plurality of individual thin wall, arcuate (e.g airfoil shaped) core elements are formed in respective master dies to have integral close tolerance mating locator features, the individual core elements are fired on ceramic supports, and the fired core elements are assembled together using the close tolerance mating features of adjacent core elements mating with one another in a manner to effect proper core element positioning and to substantially prevent penetration of molten metal between the mated features during casting. A fugitive material, such as molten wax, is applied at various locations of the core elements after assembly to hold them in position until a fugitive pattern followed by a ceramic shell mold are formed thereabout. The core assembly described above pursuant to the invention can comprise a subassembly of an aggregate core assembly used to produce complex air cooling passages in a gas turbine airfoil, such as a turbine blade or vane.
The multi-wall ceramic core assembly or portion thereof so produced comprises the plurality of spaced apart thin wall, arcuate (e.g airfoil shaped) core elements located relative to one another by the mating locator features in close tolerance fit.
The present invention is advantageous in that the ceramic core elements can be formed with the close tolerance mating locator features by conventional injection or transfer molding using appropriate ceramic compounds, in that firing of the core elements improves their dimensional integrity and permits their inspection prior to assembly to improve yield of acceptable ceramic core assemblies and reduces core assembly costs as a result, and in that high dimensional accuracy and repeatability of core assemblies is achievable without the need for ceramic adhesive between the core elements.